While a significant effort is being undertaken by the Human-Computer Interaction community in order to extend current knowledge about how users interact with computing devices and how to design and evaluate new interaction techniques, very little has been done to improve the reliability of software offering such interaction techniques. However, malfunctions and failures occur in interactive systems leading to incidents or accidents that, in aviation for instance, are [22] 80% of the time attributed to human error demonstrating the inadequacy between the system and its operators. As an error may have a huge impact on human life, strong requirements are usually set both on the final system and on the development process itself. Interactive safety-critical systems have to be designed taking into account on an equal basis several properties including usability, reliability and operability while their associated design process is required to handle issues such as scalability, verification, testing and traceability. However, software development solutions in the area of critical systems are not adequate leading to defects especially when the interactive aspects are considered. Additionally, the training program development is always designed independently from the system development leading to operators trained with inadequate material. In this paper we propose a new iterative design process embedding multiple design and modeling techniques (both formal and informal) advocated by HCI and dependable computing domains. These techniques have been adapted and tuned for interactive systems and are used in a synergistic way in order to support the integration of factors such as usability, dependability and operability and at the same time in order to deal with scalability, verification and traceability.